1. Field of the Invention
The present invention relates to a motion picture encoding device and method, a motion picture decoding device and method, a motion picture recording device, program, and data structure, using interframe prediction technology.
2. Description of the Related Art
Currently, the motion picture MPEG (Motion Picture Experts Group) format is used in general as technology for compression coding, and the data structure is publicly known. For example, the data structure in the MPEG format is described in Japanese Unexamined Patent Application Publication No. 2003-179931.
To describe the outline, in the MPEG format, each frame (picture) constituting a motion picture is classified into three types of pictures—an I picture (Intra-coded picture or Intra-frame coded picture), a P picture (Predictive coded picture), and a B picture (Bi-directionally predictive coded picture)—and is subsequently encoded.
The I picture is a picture of at least one sheet to be arranged within a GOP (Group Of Picture) wherein predefined sheets of picture data are collected to maintain the independence of the GOP. This I picture is encoded (Intra-frame coded) from only information of the frame without using interframe prediction. The P picture, on the other hand, is a predictive picture (Interframe predictive-coded) composed by regarding an I picture or a P picture in the past as a reference picture from which unidirectional motion is predicted for encoding. In addition, the B picture is a predictive picture (Bi-directional predictive coded) composed by regarding a previous or subsequent I picture or P picture located on a time axis as a reference picture from which bidirectional motion is predicted for encoding. More precisely, the P picture and B picture are represented by motion vectors (MV) obtained by a unit of a microblock with 16×16 pixels and by data of the encoding DCT (Discrete Cosine Transform) coefficient of a differential picture (predictive error) when the predictive picture is compared with a frame (actual picture) of the same timing.
During the playback time of a motion picture that has been compression-encoded in the MPEG format, as for the I picture, decoding is executed to be returned to the picture data on the original time axis. As for the P picture and B picture, the predictive error is obtained via decoding and reverse DCT conversion, and at the same time, a predictive picture is created regarding the previously decoded other frames (a past frame in the P picture, a past and a future frame in the B picture) as a reference picture with use of this reference picture and the motion vectors (MV). The picture data of the original time axis is to be created from the created predictive picture and the predictive error.
As described above, during the playback time of the motion picture that has been compression-encoded in the MPEG format, in order to cause the P picture and B picture to become displayable picture data, it is inevitable to perform processes such as decoding, reverse DCT conversion, and creation of a predictive picture for a series of frames starting from an I picture, which is referred directly or indirectly from these frames (pictures) as a starting point.
Therefore, in the case of display by frame thinning, a process of decoding, etc., had to be performed also for unnecessary frames (P pictures and/or B pictures) that are not actually subject to display. In other words, there was a problem of extremely low processing efficiency in the event of motion picture playback accompanying frame thinning.
FIGS. 24A to 24C are conceptual diagrams that describe these problems. FIG. 24A shows an I picture (I0), P pictures (P1, P2, P3, . . . ) that use it as a starting point, and the reference pictures to be referenced for encoding each P picture, all within the encoded data of a motion picture based on the MPEG format. FIG. 24B shows the presence/absence of the decoding process as well as the display of each frame in cases in which both frame rates at the time of recording and playback are 240 fps (when frame thinning is not performed). FIG. 24C shows the presence/absence of the decoding process as well as the display of each frame in cases in which the frame rate at the time of playback is 60 fps (when frame thinning is performed). Furthermore, FIGS. 24A to 24C are examples of frame sections without the presence of a B picture. Although not illustrated, in the event of creating a B picture, the frame of either the I picture or P picture located before and after on the time axis is referenced.
As shown in FIGS. 24B and 24C, when a motion picture is subjected to playback by performing frame thinning, because data processing that is equivalent to a case in which frame thinning is not performed requires the wasteful consumption of electrical power. Furthermore, in a constitution in which motion picture playback with frame thinning is performed by a CPU (Central Processing Unit), etc., with the use of predefined software, the processing load of the CPU, etc., is significant. Therefore, other processes that may be executed in parallel to motion picture playback are limited, leading to the necessity of maintaining excessive processing capability in the CPU, etc., to make the predefined processes executable parallel to the motion picture playback.
The present invention has been conducted in view of such conventional problems, and the purpose thereof is to provide a motion picture encoding device as well as a motion picture encoding method capable of obtaining encoded data of a motion picture that may efficiently perform motion picture playback accompanying frame thinning, a motion picture decoding device as well as a motion picture decoding method capable of decoding the above encoded data, and a motion picture recording device capable of recording the captured motion picture as encoded data as described above, and a program and data structure used for realizing these.